We have a bunch of Metabo grinders at work and they seem to hold up pretty well. So do the older DeWalt grinders. But no electric grinder is going to really take the kind of abuse metal fabrication can really dish out. AIR grinders are where it's at and unfortunately, so is the price.

I had an Atlas Copco LSV38-ST12-125 5" angle grinder for a demo. It was really a 4-1/2" grinder that would also squeeze in 5" wheels, and it was very easy to handle as the body diameter was much smaller than any electric grinder.
The air motor contained a governor that would maintain wheel rpm as load was applied. This, in theory, will make the consumables last longer and perform better. All I know is that it had an insane amount of power and you'd better make sure the wheel was on TIGHT and also have the wheel retainer lock installed. When releasing the trigger fully, the wheel stops NOW, and I had the wheel spin right off and dance across the shop floor for a LOOOONG way. :ashamed:
So why doesn't everyone have one??? Two problems - a $900 price tag and enormous air consumption - somewhere between 30 and 50 cfm! I've got a couple of 100hp compressors at work that will do the job, but there aren't many small shops that have that much air available. But one air grinder, provided it is properly lubricated (both the air motor and the gearbox), will outlast many electric grinders and probably save money in the long run.
Therefore, I'll keep using my $20 Tool Shop brand grinder from Menards that has performed way beyond what I expected of it and still runs great. One tip - most of these grinders (especially the cheap ones) use some sort of Mongolian Yak fat for grease. It is way too thick for the high speed gears and causes excess heating. I clean this out and replace it with Mystik synthetic blend grease as it has a rather light base oil viscosity of around 68 cSt. Most other greases have base oil viscosity in the 180-220 range, and some are over 600. This is not the same as #1, #2, etc. grade grease. You can have a "thin" grease with thick base oil and vice versa. Electric motor bearing grease is another good type - usually with base oil in the 100 cSt range like Mobilith SHC 100.
Chris